The present invention related to photothermographic material, and an image recording method and image forming method by the use thereof.
In the field of graphic arts and medical treatment, there have concerns in processing of photographic films with respect to effluents produced from wet-processing of image forming materials, and recently, reduction of the processing effluent is strongly demanded in terms of environmental protection and space saving. There has been desire a photothermographic material for photographic use, capable of forming distinct black images exhibiting high sharpness, enabling efficient exposure by means of a laser imager or a laser image setter.
Known as such a technique is a thermally developable photothermographic material which comprises on a support an organic silver salt, light sensitive silver halide grains, reducing agent and a binder, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075, and D. H. Klosterboer xe2x80x9cThermally Processed Silver Systemsxe2x80x9d (Imaging Processes and Materials) Neblette, 8th Edition, edited by Sturge, V. Walworth, and A. Shepp, page 279, 1989), etc.
Such a photothermographic material is characterized in that light sensitive silver halide grains and an organic silver salt are incorporated in a light sensitive layer as a photosensor and a silver ion source, respectively, which are thermally developed by an included reducing agent at a temperature of 8xe2x88x92 to 140xc2x0 C. to form images, without being fixed. To achieve smoothly supplied silver ions to silver halide and prevent lowered transparency caused by light scattering, there have been made attempts to improve the shape of organic silver salt grains capable of being optimally arranged in the light sensitive layer and having little adverse effect on light scattering.
However, problems arose with attempts to form fine particles simply by dispersion or pulverization at high energy using a dispersing machine, due to the fact that silver halide grains or organic silver salt grains were damaged, resulting in not only increased fogging and reduced sensitivity but also deteriorated image quality. Accordingly, there have been desired techniques of achieving enhanced photosensitivity, higher density and reduced fogging without an increase of a silver coverage.
Further, problems arose with pre-exposure storage of photothermographic materials such that variation in sensitivity, fog density or contrast occurred and problems also arose with post-process storage that the fogging or image color tone was varied. There have been made various attempts but they are still insufficient, therefore, further enhanced improvement is desired.
It is an object of the present invention to provide a photothermographic material exhibiting enhanced sensitivity and reduced fogging, causing no deterioration in image quality due to a white spots or coagula and also improved in raw stock stability (i.e., pre-exposure stock keeping) and silver image lasting quality; and an image recording method and image forming method by the use of the same.
The above object of the invention can be accomplished by the following constitution:
1. A photothermographic material comprising an organic silver salt and a light sensitive silver halide, wherein the photothermographic material contains a hydrophilic binder of 0.5 to 2 g per mol of the organic silver salt and the organic silver salt being formed in the presence of the silver halide of 7xc3x971015 to 3xc3x971017 grains per mol of the organic silver salt;
2. A method of preparing a photothermographic material comprising the steps of:
(a) preparing a light sensitive layer composition and
(b) coating the light sensitive layer composition to form a light sensitive layer,
wherein the photothermographic material comprises an organic silver salt, a light sensitive silver halide and a hydrophilic binder, step (a) comprising forming the organic silver salt in the presence of the silver halide of 7xc3x971015 to 3xc3x971017 grains per mol of the organic silver salt and the photothermographic material containing the hydrophilic binder of 0.5 to 2 g per mol of the organic silver salt.
In this invention, the photothermographic material containing an organic silver salt, a light sensitive silver halide, a reducing agent, binder and a cross-linking agent, in which the photothermographic material contains a hydrophilic binder of 0.5 to 2.0 g per mol of the organic silver salt, and during the stage of formation of the organic silver salt, 7xc3x971015 to 3xc3x971017 grains of the light sensitive silver halide per mol of the organic silver salt are mixed to form the organic silver salt, thereby leading to a photothermographic material exhibiting enhanced sensitivity and reduced fogging, causing no deterioration in image quality due to a white spots or coagula and also improved in raw stock stability (i.e., pre-exposure stock keeping) and silver image lasting quality. In this invention, the light sensitive silver halide is preferably contained in amount of 0.8 to 2.0 g/m2, based on silver.
It is contemplated that such effects of this invention are attributed to that adjustment of a hydrophilic binder surrounding the light sensitive silver halide grains to a specified quantity leads to efficient dispersion, thereby preventing coagulation of silver halide grains and efficient supply of silver ions from the organic silver salt at the stage of thermal development.
Silver halide used in the invention functions as light sensor. Silver halide grains are preferably small in size to prevent milky-whitening after image formation and obtain superior images. The grain size is preferably not more than 0.1 xcexcm, more preferably, 0.01 to 0.1 xcexcm, still more preferably, 0.03 to 0.07 xcexcm, and most preferably 0.04 to 0.07 xcexcm. The form of silver halide grains is not specifically limited, including cubic or octahedral, regular crystals and non-regular crystal grains in a spherical, bar-like or tabular form. Halide composition thereof is not specifically limited, including any one of silver chloride, silver chlorobromide, silver iodochlorobromide, silver bromide, silver iodobromide, and silver iodide.
In this invention, silver halide grains are used in an amount of 7xc3x971015 to 3xc3x971017 grains per mol of organic silver salt. The silver halide grains less than this range by number results in insufficient densities and the number exceeding this range leads to deteriorated image quality.
In this regard, the number of silver halide grains can be determined based on the density, specific gravity and size of the silver halide grains. The grain size can be determined by an electron microscope.
Silver halide used in this invention preferably occludes ions of metals belonging to Groups 6 to 11 of the Periodic Table. Preferred as the metals are W; Fe, Co, Ni, Cu, Ru, Rh, Pd, Re, Os, Ir, Pt and Au. Of these preferred are Fe, Co, Ru, Rh, Re, Os, and Ir. These metals may be introduced into silver halide in the form of a complex. In the present invention, regarding the transition metal complexes, six-coordinate complexes represented by the general formula described below are preferred:
Formula: (ML6)m: 
wherein M represents a transition metal selected from elements in Groups 6 to 11 of the Periodic Table; L represents a coordinating ligand; and m represents 0, 1-, 2-, 3-or 4-. Exemplary examples of the ligand represented by L include halides (fluoride, chloride, bromide, and iodide), cyanide, cyanato, thiocyanato, selenocyanato, tellurocyanato, azido and aquo, nitrosyl, thionitrosyl, etc., of which aquo, nitrosyl and thionitrosyl are preferred. When the aquo ligand is present, one or two ligands are preferably coordinated. L may be the same or different. Particularly preferred examples of M include rhodium (Rh), ruthenium (Ru), rhenium (Re), iridium (Ir) and osmium (Os).
Exemplary examples of transition metal ion complexes are shown below.
1: [RhCl6]3xe2x88x92
2: [RuCl6]3xe2x88x92
3: [ReCl6]3xe2x88x92
4: [RuBr6]3xe2x88x92
5: [OsCl6]3xe2x88x92
6: [IrCl6]4xe2x88x92
7: [Ru(NO)Cl5]2xe2x88x92
8: [(RuBr4(H2O)]2xe2x88x92
9: [Ru(NO) (H2O)Cl4]xe2x88x92
10: [RhCl5(H2O)]2xe2x88x92
11: [Re(NO)Cl5]2xe2x88x92
12: [Re(NO)(CN)5]2 
13: [Re(NO)Cl(CN)4]2xe2x88x92
14: [Rh(NO)2Cl4]xe2x88x92
15: [Rh(NO) (H2O)Cl4]xe2x88x92
16: [Ru(NO) (CN)5]2xe2x88x92
17: [Fe(CN)6]3xe2x88x92
18: [Rh(NS)Cl5]2xe2x88x92
19: [Os(NO)Cl5]2xe2x88x92
20: [Cr(NO) Cl5]2xe2x88x92
21: [Re(NO)C15]xe2x88x92
22: [Os(NS)Cl4(TeCN)]2xe2x88x92
23: [Ru(NS)Cl5]2xe2x88x92
24: [Re(NS) Cl4(SeCN)]2xe2x88x92
25: [Os(NS)Cl(SCN)4]2xe2x88x92
26: [Ir(NO) Cl5]2xe2x88x92
27: [Ir(NS) Cl5]2xe2x88x92
One type of these metal ions or complex ions may be employed and the same type of metals or the different type of metals may be employed in combinations of two or more types. Generally, the content of these metal ions or complex ions is suitably between 1xc3x9710xe2x88x929 and 1xc3x9710xe2x88x922 mole per mole of silver halide, and is preferably between 1xc3x9710xe2x88x928 and 1xc3x9710xe2x88x924 mole.
Compounds, which provide these metal ions or complex ions, are preferably incorporated into silver halide grains through addition during the silver halide grain formation. These may be added during any preparation stage of the silver halide grains, that is, before or after nuclei formation, a growth, physical ripening, and chemical ripening. However, these are preferably added at the stage of nuclei formation, growth, and physical ripening; furthermore, are preferably added at the stage of nuclei formation and growth; and are more preferably added during the stage of growth of from xc2xd of the grain volume to the final grain (still more preferably during the stage of growth of from xc2xe of the grain volume to the final grain). Herein, the expression xe2x80x9cadded during the stage of growth of from xc2xd of the grain volume to the final grainxe2x80x9d means addition in the process of grain growth of from the site accounting for 50% of the grain volume to the grain surface.
These compounds may be added several times by dividing the addition amount. Uniform content in the interior of a silver halide grain can be carried out. As disclosed in JP-A No. 63-29603, 2-306236, 3-167545, 4-76534, 6-110146, 5-273683, the metal can be non-uniformly occluded in the interior of the grain.
These metal compounds can be dissolved in water or a Unsuitable organic solvent (for example, alcohols, ethers, glycols, ketones, esters, amides, etc.) and then added. Furthermore, there are methods in which, for example, an aqueous metal compound powder solution or an aqueous solution in which a metal compound is dissolved along with NaCl and KCl is added to a water-soluble silver salt solution during grain formation or to a water-soluble halide solution; when a silver salt solution and a halide solution are simultaneously added, a metal compound is added as a third solution to form silver halide grains, while simultaneously mixing three solutions; during grain formation, an aqueous solution comprising the necessary amount of a metal compound is placed in a reaction vessel; or during silver halide preparation, dissolution is carried out by the addition of other silver halide grains previously doped with metal ions or complex ions. Specifically, the preferred method is one in which an aqueous metal compound powder solution or an aqueous solution in which a metal compound is dissolved along with NaCl and KCl is added to a water-soluble halide solution. When the addition is carried out onto grain surfaces, an aqueous solution comprising the necessary amount of a metal compound can be placed in a reaction vessel immediately after grain formation, or during physical ripening or at the completion thereof or during chemical ripening.
Silver halide grain emulsions used in the invention may be desalted after the grain formation, using the methods known in the art, such as the noodle washing method and flocculation process.
Silver halide emulsions used in the invention can be prepared according to the methods described in P. Glafkides, Chimie Physique Photographique (published by Paul Montel Corp., 19679; G. F. Duffin, Photographic Emulsion Chemistry (published by Focal Press, 1966); V. L. Zelikman et al., Making and Coating of Photographic Emulsion (published by Focal Press, 1964). Any one of acidic precipitation, neutral precipitation and ammoniacal precipitation is applicable and the reaction mode of aqueous soluble silver salt and halide salt includes single jet addition, double jet addition and a combination thereof. For example, silver halide emulsions are prepared by mixing an aqueous silver salt solution with an aqueous halide solution in a protective colloidal solution as a reaction mother liquor perform nucleation and crystal growth, in which the silver salt and halide solutions are generally added by double jet addition. Specifically, the controlled double jet addition is representative, in which the solutions are mixed with controlling the pAg and pH. Various variations are included therein, such as a two-step process, in which after forming seed crystal grins (or nucleation), growth is successively performed under identical or different conditions (crystal growth or ripening). Thus, controlling various factors such as crystal habit or crystal sizes by regulating mixing condition in the process of mixing silver salt and halide solutions in an aqueous protective colloid solution is well known in the art. Subsequently to the mixing process, the desalting process is performed to remove soluble salts from the emulsion. As a known representative desalting process is a flocculation method, in which a coagulant is added to the prepared silver halide emulsion to cause silver halide grain to be flocculated and separated from the supernatant containing soluble salts. After decanting the supernatant, the coagulated gelatin containing silver halide grains is re-dispersed and then, flocculation and decantation are repeated to remove any remaining salts. There is also known a desalting method by ultrafiltration, in which unwanted low-molecular weight substances such as aqueous soluble salts can be removed using an ultrafiltration membrane such as a synthetic membrane which prevents permeation of macro-molecular weight substances such as silver halide grains and gelatin.
The hydrophilic binder may be contained in any layer of the photothermographic material and preferably at least in the layer containing the organic silver salt, in an amount of 0.5 to 2.0 g per mol of organic silver salt. The hydrophilic binder is a binder which is water-soluble or capable of being present in a colloidal form, and preferably is a binder capable of functioning as a protective colloid for silver halide grains in an aqueous solution. Hydrophilic binders usable in this invention include, for example, gelatin and water soluble polymers such as polyamide compounds and polyvinyl pyrrolidine compounds. Of these, gelatin is preferred.
There is needed 0.5 to 2.0 g of the hydrophilic binder per one mol of an organic silver salt to achieve the advantageous effects of this invention. In addition to being contained together with the silver halide grains, the hydrophilic binder may further be added at the stage of forming or dispersing the organic silver salt to adjust the content thereof. Insufficiency the hydrophilic binder results in incomplete dispersion of the organic silver salt and tendency for the salt to coagulate, leading to fogging, lowered covering power and deteriorated image quality caused by white spots or coagula. An excessive hydrophilic binder often inhibits adsorption of a dye or the like, resulting in insufficient sensitivity. The amount of the hydrophilic binder contained with light sensitive silver halide is Preferably not more than 40 g per mol of silver, and more preferably not more than 35 g per mol of silver. The binder content in a photothermographic material can be determined by methods currently known in the art. Specifically, the gelatin content can be determined in accordance with the procedure of hydrolysis with hydrochloric acid, concentration and dilution with a sodium citrate buffer solution, followed by amino acid analysis.
The thus formed photosensitive silver halide can be chemically sensitized with a sulfur containing compound, gold compound, platinum compound, palladium compound, silver compound, tin compound, chromium compound or their combination. The method and procedure for chemical sensitization are described in U.S. Pat. No. 4,036,650, British Patent 1,518,850, JP-A 51-22430, 51-78319 and 51-81124. As described in U.S. Pat. No. 3,980,482, a low molecular weight amide compound may be concurrently present to enhance sensitivity at the time of converting a part of the organic silver salt to photosensitive silver halide.
In this invention, it is preferred to conduct chemical sensitization with an organic sensitizer containing a chalcogen atom. The organic sensitizer containing a chalcogen atom preferably contains a group for promoting adsorption onto silver halide and a labile chalcogen atom.
Such organic sensitizers are those having various structures, as described in JP-A 60-150046, JP-A 4-109240 and 11-218874. Specifically, a compound represented by formula (S) is preferred, having a structure in which a chalcogen atom is attached a carbon atom or a phosphorus atom through a double bond: 
wherein A1 represents an atomic group capable of being adsorbed onto silver halide; L1 represents a bivalent linkage group; Z1 represents an atomic group containing a labile chalcogen atom site; W1, W2 and W3 each represent a carboxylic acid group, sulfonic acid group, sulfinic acid group, phosphoric acid group, phosphorus acid group or a boric acid group; m1 is 0 or 1; n1 is an integer of 1 to 3; 11, 12 and 13 each are an integer of 0 to 2, provided that 11, 12 and 13 may be 0 at the same time, i.e., an aqueous solubility-promoting group as defined above (W1, W2 and W3) may not be contained.
Examples of the atomic group capable of being adsorbed onto silver halide, represented by A1 include an atomic group containing a mercapto group (e.g., mercaptooxadiazole, mercapotetrazole, mercaptotriazole mercaptodiazole, mercaptothiazole, mercaptpthiadiazole, mercaptooxazole, mercaptoimidazole, mercaptobenzthiazole, mercaptobenzoxazole, mercaptobenzimidazole, mercaptotetrazaindene, mercaptopyridyl, mercaptoquinilyl, 2-mercaptopyridyl, mercaptophenyl, mercaptonaphthyl, etc.), an atomic group containing a thione group (e.g., thiazoline-2-thione, oxazoline-2-thione, imidazoline-2-thione, benzothiazoline-2-thione, benzimidazoline-2-thione, thiazolidine-2-thione, etc.), an atomic group capable of forming an imino-silver (e.g., triazole, tetrazole, benztriazole, hydroxyazaindene, benzimidazole, indazole, etc.), and an atomic group containing an ethenyl group {e.g., 2-[N-(2-propenyl)amino]benzthiazole, N-(2-propenyl)carbazole, etc.}.
The atomic group containing a labile chalcogen atom site represented by Z1 refers to a compound group capable of forming a chalcogen silver in the presence of silver nitrate. The atomic group containing a labile chalcogen atom site preferably has a structure containing a chalcogen atom attached to a carbon atom or phosphorus atom through a double bond, in which the chalcogen atom refers to a sulfur atom, selenium atom or a tellurium atom. Examples of the atomic group containing a labile sulfur atom site include an atomic group containing a thiourea group (e.g., N,Nxe2x80x2-diethylthiourea, N-ethyl-Nxe2x80x2-(2-thiazolyl)thiourea, N,Nxe2x80x2-dimethylthiourea, N-phenylthiourea, etc.), an atomic group containing a thioamido group (e.g., thiobenzamide, thioacetoamide, etc.), polysufide, an atomic group containing a phosphine sulfide group [e.g., bis (pentafluorophenyl)phenylphosphine sulfide, diethylphosphine sulfide, dimethylphenylphosphine sulfide, etc.], and an atomic group containing a thiooxoazolidinone group (e.g., ethylrhodanine, 5-benzylidene-3-ethylrhodanine, 1,3-diphenyl-2-thiohydantoine, 3-ethyl-4-oxooxazolidine-2-thione, etc.). Examples of the atomic group containing a labile selenium atom site include an atomic group containing a selenourea group (e.g., N,Nxe2x80x2-dimethylselenourea, selenourea, N-acetyl-N,Nxe2x80x2-diethylselenourea, N-trifluoroacetyl-Nxe2x80x2,Nxe2x80x2-dimethylselenourea, N-ethyl-Nxe2x80x2-(2-thiazolyl)selenourea, N,Nxe2x80x2-diphenylselenourea, etc.), an atomic group containing a selenoamido group (e.g., N-methyl-selenobenzamide, N-phenyl-selenobenzamide, N-ethyl-selenobenzamide, etc.), an atomic group containing a phosphine selenide [e.g., triphenyl-phosphine selenide, diphenyl(entafluorophenyl)phosphine selenide, tris(m-chlorophenyl)phosphine selenide, etc.], an atomic group containing selenophosphate group [e.g., tris(p-tolyl)selenophosphate, etc.], an atomic group containing a selenoester group (e.g., p-methoxyselenobenzoic acidxe2x95x90O-isopropylester, selenobenzoic acid=Se-(3xe2x80x2-oxobutyl)ester, p-methoxyselenobenzoic acidxe2x95x90Se-(3xe2x80x2 oxocyclohexyl)ester, etc.), an atomic group containing a selenide group [e.g., bis(2,6-dimethoxybenzoyl)selenide, bis(n-butoxycarbonyl)selenide, bis(benzyloxycarbonyl)selenide, bis(N,N-dimethylcarbamoyl)selenide, etc.], an atomic group containing triselenane group [e.g., 2,4,6-ris(p-methoxyphenyl)triselenane, etc.], and an atomic group containing aselenoketone group (e.g., 4-methoxyselenoacetophenone, 4,4-methoxyselenobenzophenone, etc.). Examples of the atomic group containing a labile tellurium atom site include an atomic group containing a phosphine telluride group (e.g., butyl-di-isopropylphosphine telluride, triscyclohexylphosphine telluride, etc.), an atomic group containing a tellurourea group (e.g., N,Nxe2x80x2-diethyl-N,Nxe2x80x2-diethylenetelluorourea, N,Nxe2x80x2-dimethylene-N,Nxe2x80x2-dimethyltellyrourea, etc.), an atomic group containing a telluoroamido group [e.g., N,N-dimethyl-tellurobenzamide, N,N-tetramethylene-(p-tolyl)tellurobenzamide], an atomic group containing a tellurophosphate group [e.g., tris(p-tolyl)tellurophosphate, trisbutyltellurophosphate, etc.], and an atomic group containing a telluophosphoric amido group (e.g., hexamethyltellurophosphoric amide, etc.).
The atomic group containing a labile selenium or tellurium atom can also be selected from the compounds described in JP-A Nos. 4-25832, 4-109240, 4-147250, 4-33043, 5-40324, 5-24332, 5-24333, 5-303157, 5-306268, 5-306269, 6-27573, 6-43576, 6-75328, 6-17528, 6-180478, 6-17529, 6-208184, 6-208186, 6-317867, 7-92599, 7-98483, 7-104415, 7-140579, and 7-301880.
The chalcogen atom-containing organic sensitizers used in this invention may contain an aqueous solubility-promoting group. Examples of the aqueous solubility-promoting group include a carboxylic acid group, sulfonic acid group, sulfinic acid group, phosphoric acid group, phosphorus acid group or a boric acid group. The chalcogen atom-containing organic sensitizers used in this invention may contain a group capable of being adsorbed onto silver halide and a labile chalcogen atom site. The group capable of being adsorbed onto silver halide and the labile chalcogen atom site may be linked directly or through a linkage group with each other. In cases where an aqueous solubility-promoting group is further contained, the aqueous solubility-promoting group, the group capable of being adsorbed onto silver halide and the labile chalcogen atom site may be linked directly or through a linkage group with each other.
The bivalent linkage group represented by L1 is a group comprising a carbon atom, hydrogen atom, oxygen atom, nitrogen atom or sulfur atom. Examples thereof an alkylene group having 1 to 20 carbon atoms (e.g., methylene, ethylene, propylene, hexylene, etc.), an arylenes group (e.g., phenylene, naphthylene, etc.), xe2x80x94CONR1xe2x80x94, xe2x80x94SO2NR2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NR3xe2x80x94, xe2x80x94NR4COxe2x80x94, xe2x80x94NR5SO2xe2x80x94, xe2x80x94NR6CONR7xe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94 and groups in which plural these groups are linked.
R1, R2, R3, R4, R5, R6, and R7 are each a hydrogen atom, an aliphatic group, an alicyclic group, an aromatic group or a heterocyclic group. The aliphatic group represented by R1, through R7 include, for example, a straight chaine or branched alkyl group having 1 to 20 carbon atoms (e.g., methyl, ethyl, isopropyl, 2-ethyl-hexyl, etc.), an akenyl group (e.g., propenyl, 3-pentenyl, 2-butenyl, cyclohexenyl, etc.), an alkynyl group (e.g., propargyl, 3-pentynyl, etc.) and an aralkyl group (e.g., benzyl, phenethyl, etc.). The alicyclic group is one having 5 to 8 carbon atoms (e.g., cyclopentyl, cyclohexyl, etc.); the aromatic group is a monocyclic or condensed ring group having 6 to 10 carbon atoms, such as phenyl or naphthyl; and the heterocyclic group an oxygen, sulfur or nitrogen containing, 5-to 7-membered monocyclic ring or ring condensed with other ring)s), such as furyl, thienyl, benzfuryl, pyrrolyl, indolyl, thiazolyl, imidazolyl, mprpholyl, piperazyl, or pyrazyl. The groups represented by R1 through R7 may be substituted with an optimal atom or group at the optimal position. Examples of the substituent atom or group include hydroxy, a halogen atom (e.g., fluorine, chlorine, bromine, iodine), cyano, amino group (e.g., metylamino, anilino, diethylamino, 2-hydroxyethylamino, etc.), acyl group (e.g., acetyl, benzoyl, propanoyl, etc.), carbamoyl group (e.g., carbamoyl, N-methylcarbamoyl, N,N-tetramethylenecarbamoyl, N-methanesulfonylcarbamoyl, N-acetylcarbamoyl, etc.), alkoxy group (e.g., methoxy, ethoxy, 20hydroxyethoxy, 2-methoxyethoxy, etc.), alkoxycarbonyl group (e.g., methoxycarbonyl, ethoxycarbonyl, 2-methoxyethoxycarbonyl, etc.), sulfonyl group (e.g., methanesulfonyl, trifluoromethanesulfonyl, benzenesulfonyl, p-toluenesulfonyl, etc.), sulfamoyl group (e.g., sulfamoyl, N,N-dimethyl-sulfamoyl, morpholinosulfamoyl, N-ethylsulfamoyl, etc.), acylamino group (e.g., acetoamide, trifluoroacetoamido, benzamido, thienocarbonylamino benzenesulfonamido, etc.), and alkoxycarbonylamino, (e.g., methoxycarbonylamino, N-methyl-ethoxycarbonylamino etc.).
W1, W2 and W3 each a carboxylic acid group, sulfonic acid group, sulfinic acid group, phosphoric acid group, phosphorus acid group or a boric acid group, each of which may be in a free form or may be a counter salt with an alkali metal, alkaline earth metal, ammonium or an organic amine.
Exemplary examples of the chalcogen atom-containing organic sensitizers usable in this invention and the compound represented by formula (S) own below but by no means limited to these 
The amount of the chalcogen atom-containing organic sensitizers to be used in this invention, depending on the kind of a chalcogen compound, light sensitive silver halide grains and the chemical sensitization environment is preferably 10xe2x88x928 to 10xe2x88x922 mol. and more preferably 10xe2x88x927 to 10xe2x88x923 mol per mol of silver halide. In this invention, the chemical sensitization environment is not specifically limited and it is preferred to conduct chemical sensitization with the chalcogen atom-containing organic sensitizer, in the presence of a compound capable of allowing silver chalcogenide or silver nuclei formed on the light sensitive silver halide grains to disappear or to be reduced in size, specifically in the presence of an oxidizing agent capable of oxidizing the silver nuclei. The preferred sensitizing condition thereof includes a pAg of 6 to 11, and more preferably 7 to 10, a pH of 5 to 8, and a temperature of 30xc2x0 C. or less. The excessively high temperature accelerates side reaction, leading to increased fogging and lowering stability of the photothermographic material. In the photothermographic material of this invention, it is therefore preferable that the light sensitive silver halide grains are chemically sensitized at a temperature of 30xc2x0 C. or less, using the chalcogen atom-containing organic sensitizer in the presence of silver nuclei formed on the grains. It is also preferred that the resulting silver halide grains are mixed with an organic silver salt, dispersed and dried.
It is also preferred to conduct chemical sensitization with the organic sensitizer in the presence of a sensitizing dye or a heteroatom-containing compound capable of being adsorbed onto silver halide. Performing chemical sensitization in the presence of the compound capable of being adsorbed onto silver halide prevents dispersion of chemical sensitization center nuclei, leading to enhanced sensitivity and minimized fogging. The preferred heteroatom containing compound capable of being adsorbed onto silver halide include nitrogen containing heterocyclic compound described in JP-A No. 3-24537. In the heteroatom-containing compound, examples of the heterocyclic ring include a pyrazolo ring, pyrimidine ring, 1,2,4-triazole ring, 1,2,3-triazole ring, 1,3,4-thiazole ring, 1,2,3-thiadiazole ring, 1, 2, 4-thiadiazole ring, 1,2,5-thiadiazole ring, 1,2,3,4-tetrazole ring, pyridazine ring, 1,2,3-triazine ring, and a condensed ring of two or three of these rings, such as triazolotriazole ring, diazaindene ring, triazaindene ring and pentazaindene ring. Condensed heterocyclic ring comprised of a monocycic hetero-ring and an aromatic ring include, for example, a phthalazine ring, benzimidazole ring indazole ring, and benzthiazole ring. Of these, an azaindene ring is preferred and hydroxy-substituted azaindene compounds, such as hydroxytriazaindene, tetrahydroxyazaindene and hydroxypentazaundene compound are more preferred. The heterocyclic ring may be substituted by substituent groups other than hydroxy group. Examples of the substituent group include an alkyl group, substituted alkyl group, alkylthio group, amino group, hydroxyamino group, alkylamino group, dialkylamino group, arylamino group, carboxy group, alkoxycarbonyl group, halogen atom and cyano group. Examples thereof are shown below but are not limited to these:
(1) 2,4-dihydroxy-6-methyl-1,3a,7-triazaindene,
(2) 2,5-dimethyl-7-hydroxy-1,4,7a-triazaindene,
(3) 5-amino-7-hydroxy-2-methyl-1,4,7a-triazaindene,
(4) 4-hydroxy-6-methyl-1,3,3a,7-tetrazaindene.
(5) 4-hydroxy-1,3,3a,7-tetrazaindene,
(6) 4-hydroxy-6-phenyl-1,3,3a,7-tetrazaindene,
(7) 4-methyl-6-hydroxy-1,3,3a,7-tetrazaindene,
(8) 2,6-dimethyl-4-hydroxy-1,3,3a,7-tetrazaindene,
(9) 4-hydroxy-5-ethyl-6-methyl-1,3,3a,7-tetrazaindene,
(10) 2,6-dimethyl-4-hydroxy-5-ethyll,3,3a,7 tetrazaindene,
(11) 4-hydroxy-5,6-dimethyl-1,3,3a,7-tetrazaindene,
(12) 2,5,6-trimethyl-4-hydroxy-1,3,3a,7-tetrazaindene,
(13) 2-methyl-4-hydroxy-6-phenyl-1,3,3a,7-tetrazaindene,
(14) 4-hydroxy-6-methyl-1,2,3a,7-tetrazaindene,
(15) 4-hydroxy-6-ethyl-1,2,3a,7-tetrazaindene,
(16) 4-hydroxy-6-phenyl-1,2,3a,7-tetrazaindene,
(17) 4-hydroxy-1,2,3a,7-tetrazaindene,
(18) 4-methyl-6-hydroxy-1,2,3a,7-tetrazaindene,
(19) 7-hydroxy-5-methyl-1,2,3,4,6-pentazaindene
(20) 5-hydroxy-7-methyl-1m2,3,4,6-pentazaindene,
(21) 5,7-dihysroxy-1,2,3,4,6-pentazaindene,
(22) 7-hydroxy-5-methyl-2-phenyl-1,2,3,4,6-pentazaindene,
(23) 5-dimethylamino-7-hydroxy-2-phenyl-1,2,3,4,6-pentazaindene.
The amount of the heterocyclic ring containing compound to be added, which is broadly variable with the size or composition of silver halide grains, is within the range of 10xe2x88x926 to 1 mol, and preferably 10xe2x88x924 to 10xe2x88x921 mol per mol silver halide.
Silver halide to be subjected to chemical sensitization may be one in the presence or in the absence of organic silver salts, or may be mixture thereof.
In one preferred embodiment of this invention, the overall process of forming light sensitive silver halide is performed at a pH of 3 to 6, more preferably 4 to 6.
The determination of transition metals occluded in the light sensitive silver halide used in this invention will be described. Distribution of the concentration of a transition metal within a silver halide grain can be determined by stepwise dissolution of the grain from the grain surface and determination of the transition metal content at each site, for example, according to the following procedure.
Prior to the determination of the transition metal, a silver halide emulsion was subjected to the following pre-treatment. To ca 30 ml of the emulsion, 50 ml of an aqueous 0.2% actinase solution was added and stirred at 40xc2x0 C. for 30 min. to perform hydrolysis of gelatin. Such procedure was repeated five times. After centrifugal separation, the r hydrolysis products were washed five times with 50 ml methanol, twice with a 1 mol/l nitric acid solution and five times with ultra-pure water, and after centrifugal separation, only the silver halide was separated. Surface portions of the thus obtained silver halide grains were dissolved with an aqueous ammonia solution or a pH-adjusted ammonia solution (in which the ammonia concentration or pH was varied in accordance with the halide composition of silver halide and the dissolution amount). Specifically, as a method for dissolving the outermost surface of silver halide grains, 2 g of the silver bromide grains can be washed to a depth of about 3% from the surface, using 20 ml of an aqueous ca. 10% ammonia solution. As a result, the amount of dissolved silver halide can be determined in such a manner that after separation of silver halide grains from the aqueous ammonia solution used for dissolving silver halide by centrifugation, the silver content of the supernatant can be determined using an inductively coupled plasma-mass spectroscopy (ICP-MS), or inductively coupled plasma-atomic emission spectroscopy (ICP-AES) or atomic absorption spectroscopy. Thus, the amount of the transition metal contained to a depth of 3% from the surface can be determined from the difference in the total metal content of silver halide grains between before and after being subjected to surface dissolution. The transition metal content can be determined by dissolution with an aqueous ammonium thiosulfate solution, aqueous sodium thiosulfate solution or aqueous potassium cyanide solution, followed by the matrix-matched ICP-MS method, ICP-AES method or atomic absorption analysis method. In the case of employing potassium cyanide as a solvent and the ICP-MS as an analysis apparatus (FISON, available from Elemental Analysis Corp.), for example, after dissolving ca. 40 mg of silver halide in 5 ml of an aqueous 0.2 mol/1 potassium cyanide solution, a solution of Cs as an internal standard element was added to form a content of 10 ppb and ultra-pure water was further added to make 100 ml to prepare a sample. Using a calibration curve matrix-fitted by using silver halide free of the transition metal, the transition metal content of the sample was determined by the ICP-MS method. In this case, the silver content of the sample can be precisely determined by subjecting the sample diluted with ultra-pure water to a factor of 100 to the ICP-AES or atomic absorption analysis. Further, the transition metal content in the interior of the silver halide grain can also be determined in the manner that after subjecting the grain surface to dissolution, the silver halide grains are washed with ultra-pure water and then the grain surface dissolution is repeated.
A transition metal doped in the peripheral region of the silver halide grain can also be determined by the foregoing method of determining the transition metal content, in combination with electron microscopic observation. In cases where plural transition metals are contained, the total content thereof are counted by mol. number.
In the embodiments of this invention, it is preferred that when the photothermographic material is subjected to light exposure of 280 xcexcJ/cm2 and thermal development at 123xc2x0 C. for 16.5 sec., not more than 25% by number (and more preferably not more than 20% by number) of the light sensitive silver halide grains having a grain diameter of 10 to 100 nm is not in contact with developed silver, thereby leading to enhanced sensitivity, lowr fogging and improved latent image stability after exposure and before thermal development.
Thermal development at 123xc2x0 C. for 16.5 sec. can be conducted by bringing the photothermographic material into contact with a thermal-developing drum heated at 123xc2x0 C. for a period of 16.5 sec.
The percentage by number of the light sensitive silver halide grains which are not in contact with developed silver can be determined in accordance with the following procedure. Thus, a thermally developed light sensitive layer coated on the support is adhered to an optimum holder, using an adhesive. Using a diamond knife, an ultra-thinned slice having a thickness of 0.1 to 0.2 xcexcm in the direction vertical to the support is prepared. The thus prepared ultra-thin slice is placed on a carbon membrane supported by a copper mesh, having been subjected to glow discharge treatment to enhance hydrophilicity and observed with a transmission electron microscope (also denoted as TEM) at a magnifying factor of 5,000 to 40,000, while cooled with liquid nitrogen to a temperature lower than xe2x88x92130xc2x0 C. The electron microscopic image is recorded by means of a photographic film, an imaging plate or a CCD camera. An optimal portion not having been broken or loose is selected. In this invention, when the distance between an organic silver salt and a silver halide grain is not more than 2 mm in the electron micrograph obtained at a magnification of 40,000, it is regarded as being in contact, and when the distance is more than 2 mm, it is regarded as not being in contact.
A carbon membrane supported by an organic membrane such as collodion or form bar is preferably used and a single carbon membrane which is obtained by forming it on a rocksalt substrate and removing the substrate by dissolution or obtained by removing the organic membrane by dissolution with an organic solvent or by ion-etching is more preferably used.
The acceleration voltage of the TEM is preferably 80 to 400 kV, and more preferably 80 to 200 kV.
The number of light sensitive silver halide grains being present within a given area, A (xcexcm2) of the recorded image is counted according to the following equation:
grain number per 1 xcexcm3=number of silver halide grains being present within a given area (A) of the recorded image/area A x slice thickness (xcexcm).
In this case, the number of the field of view is determined so as to amount to 1000 or more silver halide grains. The slice thickness can be determined in such a manner that photographed slice was warmed to room temperature, buried in epoxy resin and the section thereof was observed.
Next, a film which has been subjected to exposure of 280 xcexcJ/cm2 and thermal development at 123xc2x0 C. for 16.5 sec. is also similarly treated. Thus, the prepared a slice is observed with the TEM to count the number of silver halide grains which are not in contact with developed silver to determine the number of remaining silver halide grains. In this case, the number of the field of view is determined so as to amount to 1000 or more silver halide grains:
percent by number of silver halide grains which are not in contact with developed silver=(number of silver halide grains which are not in contact with developed silver, per 1 xcexcm3)/(number of silver halide grains/xcexcm3 in a raw film)xc3x97100.
Details of techniques for electron microscopic observation and techniques for preparing samples are referred to xe2x80x9cMedical and Biological Electron Microscopic Observationxe2x80x9d edited by NIHON DENSHIKENBIKYO GAKKAI, KANTO-SHIBU, published by MARUZEN and xe2x80x9cPreparation of Biological Samples for Electron Microscopic Observationxe2x80x9d edited by NIHON DENSHIKENBIKYO GAKKAI, KANTO-SHIBU, published by MARUZEN.
Organic silver salts used in this invention are reducible silver source, and silver salts of organic acids or organic heteroacids are preferred and silver salts of long chain fatty acid (preferably having 10 to 30 carbon atom and more preferably 15 to 25 carbon atoms) or nitrogen containing heterocyclic compounds are more preferred. Specifically, organic or inorganic complexes, ligand of which have a total stability constant to a silver ion of 4.0 to 10.0 are preferred. Exemplary preferred complex salts are described in RD17029 and RD29963, including organic acid salts (for example, salts of gallic acid, oxalic acid, behenic acid, stearic acid, palmitic acid, lauric acid, etc.); carboxyalkylthiourea salts (for example, 1-(3-carboxypropyl)thiourea, 1-(3-caroxypropyl)-3,3-dimethylthiourea, etc.); silver complexes of polymer reaction products of aldehyde with hydroxy-substituted aromatic carboxylic acid (for example, aldehydes (formaldehyde, acetaldehyde, butylaldehyde, etc.), hydroxy-substituted acids (for example, salicylic acid, benzoic acid, 3,5-dihydroxybenzoic acid, 5,5-thiodisalicylic acid, silver salts or complexes of thiones (for example, 3-(2-carboxyethyl)-4-hydroxymethyl-4-(thiazoline-2-thione and 3-carboxymethyl-4-thiazoline-2-thione), complexes of silver with nitrogen acid selected from imidazole, pyrazole, urazole, 1.2,4-thiazole, and 1H-tetrazole, 3-amino-5-benzylthio-1,2,4-triazole and benztriazole or salts thereof; silver salts of saccharin, 5-chlorosalicylaldoxime, etc.; and silver salts of mercaptides. Of these organic silver salts, silver salts of fatty acids are preferred, and silver salts of behenic acid, arachidic acid and stearic acid are specifically preferred.
The organic silver salt compound can be obtained by mixing an aqueous-soluble silver compound with a compound capable of forming a complex. Normal precipitation, reverse precipitation, double jet precipitation and controlled double jet precipitation described in JP-A 9-127643 are preferably employed. For example, to an organic acid is added an alkali metal hydroxide (e.g., sodium hydroxide, potassium hydroxide, etc.) to form an alkali metal salt soap of the organic acid (e.g., sodium behenate, sodium arachidate, etc.), thereafter, the soap and silver nitrate are mixed by the controlled double jet method to form organic silver salt crystals. In this case, silver halide grains may be concurrently present.
In the present invention, organic silver salts have an average grain diameter of 2 xcexcm or less and are monodisperse. The grain diameter of the organic silver salt as described herein is, when the organic salt grain is, for example, a spherical, cylindrical, or tabular grain, a diameter of the sphere having the same volume as each of these grains. The average grain diameter is preferably between 0.05 and 1.5 xcexcm, and more preferably between 0.05 and 1.0 xcexcm. Furthermore, the monodisperse as described herein is the same as silver halide grains and preferred monodispersibility is between 1 and 30%.
It is also preferred that at least 60% of the total of the organic silver salt is accounted for by tabular grains. The tabular grains refer to grains having a ratio of an average grain diameter to grain thickness, i.e., aspect ratio (denoted as AR) of 3 or more:
AR=diameter (xcexcm)/thickness (xcexcm)
To obtain such tabular organic silver salts, organic silver salt crystals are pulverized together with a binder or surfactant, using a ball mill. Thus, using these tabular grains, photosensitive materials exhibiting high density and superior image fastness are obtained.
To prevent hazing of the photosensitive material, the total amount of silver halide and organic silver salt is preferably 0.5 to 2.2 g/m2, leading to high contrast images. In this case, the amount is represented in terms of equivalent converted to silver. The amount of silver halide is preferably 50% by weight or less, more preferably 25% by weight or less, and still more preferably 0.1 to 15% by weight, based on the total silver amount.
Dispersion of organic silver salts used in this invention will be described. Optionally after preliminarily dispersed together with a binder or a surfactant, organic silver salt grains are preferably pulverized and dispersed by means of a media dispersing machine or a high pressure homogenizer. In the preliminary dispersion, conventional anchor-type or propeller-type stirring machine, a high-speed centrifugal radiation type stirring machine (or dissolver) or a high-speed rotational shearing type stirrer (homomixer) are employed. Examples of the media dispersing machine include a convolution mill such as a ball mill, planet ball mill or vibration ball mill, a medium-stirring mill such as beads mill or atreiter, and a basket mill. The high pressure homogenizer include a type of colliding with wall or plug, a type in which plural divided liquids are allowed to collide with each other and a type of passing through fine orifice.
Preferred examples of ceramics used for ceramic beads used in media dispersion include Al2O3, BaTiO3, SrTiO3, MgO, Zro, BeO, Cr2O3, SiO2, SiO2xe2x80x94Al2O3, Cr2O3xe2x80x94MgO, MgOxe2x80x94CaO, MgOxe2x80x94Al2O3 (spinel), SiC, TiO3, K2O, Na2O, BaO, PbO, PbO3, SrTiO3 (strontium titanate), BeAl2O4, Y3Al5O12, ZrO2xe2x80x94Y2O3 (cubic zirconia), 3BeOxe2x80x94Al2O3-6SiO2 (synthetic emerald), C (synthetic diamond), Si2O-nH2O, silicon nitride, yttrium-stabilized zirconia, zirconia-reinforced alumina. Of these, yttrium-stabilized zirconia and zirconia-reinforced alumina (hereinafter, such zirconia-containing ceramics are also called zirconia) are specifically preferred in terms of having less formation of impurities produced by friction with beads or the dispersing machine at the time of dispersion.
In apparatuses used for dispersing tabular organic silver salt grains, ceramics such as zirconia, alumina, silicon nitride and boron nitride, or diamond are preferably employed as material for the member in contact with the organic silver salt grains. Zirconia is specifically preferred.
When the foregoing dispersion is conducted, 0.1 to 10% by weight of a binder, based on organic silver salt is preferably used and the temperature is preferably maintained at not more than 45xc2x0 C. during the preliminary dispersion and the main dispersion. In the main dispersion, the high pressure homogenizer is operated twice or more at 29.42 MPa to 98.06 MPa, and in the case of employing the media dispersing machine, it is preferably operated at a circumferential speed of 6 to 13 m/sec.
Zirconia can be employed as beads or a part of a member, which may be mixed with the emulsion at the time of dispersing. Thereby, enhanced photographic performance can be achieved. Zirconia fragments may be added at the time of dispersion or preliminary dispersion. Methods therefore are not specifically limited and, for example, highly concentrated zirconia solution can be obtained by allowing methyl ethyl ketone (MEK) to circulate in a beads mill filled with zirconia beads.
In this invention, it is preferred to disperse the organic silver salt together with light sensitive silver halide in a water-miscible solvent. The water-miscible solvent refers to an organic solvent exhibiting a solubility in water of 3% by weight or more. Examples thereof include acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, isopropanol, butanol, tetrahydrofurane, dioxane, dioxirane, dimethylformamide, dimethylacetoamide, and N-methylpyrrolidone. Of these, methyl ethyl ketone is preferred.
Commonly known reducing agents are used in the photothermographic materials, including phenols, polyphenols having two or more phenols, naphthols, bisnaphthols, polyhydoxybenzenes having two or more hydroxy groups, polyhydoxynaphthalenes having two or more hydroxy groups, ascorbic acids, 3-pyrazolidones, pyrazoline-5-ones, pyrazolines, phenylenediamines, hydroxyamines, hydroquinone monoethers, hydrooxamic acids, hydrazides, amidooximes, and N-hydroxyureas. Further, exemplary examples thereof are described in U.S. Pat. Nos. 3,615,533, 3,679,426, 3,672,904, 3,51,252, 3,782,949, 3,801,321, 3,794,488, 3,893,863, 3,887,376, 3,770,448, 3,819,382, 3,773,512, 3,839,048, 3,887,378, 4,009,039, and 4,021,240; British Patent 1,486,148; Belgian Patent 786,086; JP-A 50-36143, 50-36110, 50-116023, 50-99719, 50-140113, 51-51933, 51-23721, 52-84727; and JP-B 51-35851. An optimal reducing agent can be selected from these reducing agents.
Of these reducing agents, in cases where fatty acid silver salts are used as an organic silver salt, preferred reducing agents are polyphenols in which two or more phenols are linked through an alkylene group or a sulfur atom, specifically, polyphenols in which two or more phenols are linked through an alkylene group or a sulfur atom and the phenol(s) are substituted at least a position adjacent to a hydroxy group by an alkyl group (e.g., methyl, ethyl, propyl, t-butyl, cyclohexyl) or an acyl group (e.g., acetyl, propionyl). Examples thereof include polyphenols compounds such as 1,1-bis(2-hydroxy-3,5-dimethylphenyl)-3,5,5-trimethylhexane, 1,1-bis(2-hydroxy-3-t-butyl-5-methyphenyl)methane, 1,1-bis(2-hydroxy-3,5-di-t-butylphenyl)methane, 2-hydroxy-3-t-butyl-5-methylphenyl)-(2-hydroxy-5-methylphenyl)methane, 6,6xe2x80x2-benzylidene-bis(2,4-di-t-butylphenol), 6,6xe2x80x2-benzylidene-bis(2-t-butyl-4-methylphenol), 6,6xe2x80x2-benzylidene-bis(2,4-dimethylphenol), 1,1-bis(2-hydroxy-3,5-dimethylphenyl)-2-methylpropane, 1,1,5,5-tetrakis(2-hydroxy-3,5-dimethylphenyl)-2,4-ethylpentane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 2,2-bis (4-hydroxy-3,5-di-t-butylphenyl)propane, as described in U.S. Pat. No. 3,589,903 and 4,021,249, British Patent 1,486,148, JP-A 51-51933, 50-36110 and 52-84727 and JP-B 51-35727; bisnaphthols described in U.S. Pat. No. 3,672,904, such as 2,2xe2x80x2dihydoxy-1,1xe2x80x2-binaphthyl, 6,6xe2x80x2-dibromo-2,2xe2x80x2-dihydroxy-1,1xe2x80x2-binaphthyl, 6,6xe2x80x2-dinitro-2,2xe2x80x2-dihydroxy-1,1xe2x80x2-binaphtyl, bis(2-hydroxy-l-2 naphthyl)methane, 4,41-dimethoxy-l,1xe2x80x2-dihydroxy-2,2xe2x80x2-binaphthyl; sulfonamidophenols or sulfonamidonaphthols described in U.S. Pat. No. 3,801,321, such as 4-benzenesulfonamidophenol, 2-benzenesulfonamidophenol, 2,6-dichloro-4-benzenesulfonamidophenol and 4-benzenesulfonamidonaphthol.
The photothermographic material preferably contains, in addition to the foregoing components, an additive, which is called an image toning agent, color tone providing agent or activator toner (hereinafter, called an image toning agent). The image toning agent concerns oxidation-reduction reaction of an organic silver salt with a reducing agent, having a function of increasing color of the formed silver image or making it black. Image toning agents are preferably incorporated into the photothermographic material used in the present invention. Examples of preferred image toning agents are disclosed in Research Disclosure Item 17029, and include the following:
imides (for example, phthalimide), cyclic imides, pyrazoline-5-one, and quinazolinone (for example, succinimide, 3-phenyl-2-pyrazoline-5-on, 1-phenylurazole, quinazoline and 2,4-thiazolidione); naphthalimides (for example, N-hydroxy-1,8-naphthalimide); cobalt complexes (for example, cobalt hexaminetrifluoroacetate), mercaptans (for example, 3-mercapto-1,2,4-triazole); N-(aminomethyl)aryldicarboxyimides [for example, N-(dimethylaminomethyl)phthalimide]; blocked pyrazoles, isothiuronium derivatives and combinations of certain types of light-bleaching agents (for example, combination of N,Nxe2x80x2-hexamethylene(1-carbamoyl-3,5-dimethylpyrazole), 1,8-(3,6-dioxaoctane)bis-(isothiuroniumtrifluoroacetate), and 2-(tribromomethyl-sulfonyl)benzothiazole; merocyanine dyes (for example, 3-ethyl-5-((3-etyl-2-benzothiazolinylidene-(benzothiazolinylidene))-l-methylethylidene-2-thio-2,4-oxazolidinedione); phthalazinone, phthalazinone derivatives or metal salts thereof (for example, 4-(l-naphthyl)phthalazinone, 6-chlorophthalazinone, 5,7-dimethylphthalazinone, and 2,3-dihydro-1,4-phthalazinedione); combinations of phthalazinone and sulfinic acid derivatives (for example, 6-chlorophthalazinone and benzenesulfinic acid sodium, or 8-methylphthalazinone and p-trisulfonic acid sodium); combinations of phthalazine and phthalic acid; combinations of phthalazine (including phthalazine addition products) with at least one compound selected from maleic acid anhydride, and phthalic acid, 2,3-naphthalenedicarboxylic acid or o-phenylenic acid derivatives and anhydrides thereof (for example, phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid, and tetrachlorophthalic acid anhydride); quinazolinediones, benzoxazine, naphthoxazine derivatives, benzoxazine-2,4-iones (for example, 1,3-benzoxazine-2,4-dione); pyrimidines and asymmetry-triazines (for example, 2,4-dihydroxypyrimidine), and tetraazapentalene derivatives (for example, 3,6-dimercapto-1,4-diphenyl-1H,4H-2,3a,5,6a-tatraazapentalene) Preferred image color control agents include phthalazone or phthalazine.
Binders other than the binder used in the formation of organic silver salts. Binders used in the image forming layer are transparent or translucent and generally colorless, including natural polymers, synthetic polymers or copolymers and film forming mediums. Exemplary examples thereof include gum Arabic, polyvinyl alcohol, hydroxyethyl cellulose, cellulose acetate, cellulose acetate butyrate, polyvinyl pyrrolidine, casein, starch, polyacrylic acid, poly(methyl methacrylate), poly(methylmethacrylic acid), polyvinyl chloride, polymethacrylic acid, copoly(styrene-anhydrous maleic acid), copoly(styrene-acrylonitrile), copoly(styrene-butadiene9, polyvinyl acetals (e.g., polyvinyl formal, polyvinyl butyral), polyesters, polyurethanes, phenoxy resin, polyvinylidene chloride, polyepoxides, polycarbonates, polyvinyl acetate, cellulose esters, and polyamides, these of which may be hydrophilic or hydrophobic. Of these binders, water insoluble polymers are preferred such as cellulose acetate, cellulose acetate-butyrate and polyvinyl butyral, and polyvinyl butyral is more preferred.
Ad The binder content in the light sensitive layer is preferably 1.5 to 6 g/m2, and more preferably 1.7 to 5 g/m2. The content of less than 1.5 g/m2 often results in an increase in density of the unexposed area to levels unacceptable in practical use.
In the present invention, a matting agent is preferably incorporated into the image forming layer side. In order to minimize the image abrasion after thermal development, the matting agent is provided on the surface of a photosensitive material and the matting agent is preferably incorporated in an amount of 0.5 to 30 percent in weight ratio with respect to the total binder in the emulsion layer side.
In cases where a non photosensitive layer is provided on the opposite side of the support to the photosensitive layer, it is preferred to incorporate a matting agent into at least one of the non-photosensitive layer (and more preferably, into the surface layer) in an amount of 0.5 to 40% by weight, based on the total binder on the opposite side to the photosensitive layer.
Materials of the matting agents employed in the present invention may be either organic substances or inorganic substances. Examples of the inorganic substances include silica described in Swiss Patent No. 330,158, etc.; glass powder described in French Patent No. 1,296,995, etc.; and carbonates of alkali earth metals or cadmium, zinc, etc. described in U.K. Patent No. 1.173,181, etc. Examples of the organic substances include starch described in U.S. Pat. No. 2,322,037, etc.; starch derivatives described in Belgian Patent No. 625,451, U.K. Patent No. 981,198, etc.; polyvinyl alcohols described in Japanese Patent Publication No. 44-3643, etc.; polystyrenes or polymethacrylates described in Swiss Patent No. 330,158, etc.; polyacrylonitriles described in U.S. Pat. No. 3,079,257, etc.; and polycarbonates described in U.S. Pat. No. 3,022,169.
The shape of the matting agent may be crystalline or amorphous. However, a crystalline and spherical shape is preferably employed. The size of a matting agent is expressed in the diameter of a sphere having the same volume as the matting agent. The particle diameter of the matting agent in the present invention is referred to the diameter of a spherical converted volume. The matting agent employed in the present invention preferably has an average particle diameter of 0.5 to 10 xcexcm, and more preferably of 1.0 to 8.0 xcexcm. Furthermore, the variation coefficient of the size distribution is preferably not more than 50 percent, is more preferably not more than 40 percent, and is most preferably not more than 30 percent. The variation coefficient of the size distribution as described herein is a value represented by the formula described below:
(Standard deviation of particle diameter)/(average particle diameter)xc3x97100 
The matting agent according to the present invention can be incorporated into any layer. In order to accomplish the object of the present invention, the matting agent is preferably incorporated into the layer other than the light sensitive layer, and is more preferably incorporated into the farthest layer from the support.
Addition methods of the matting agent include those in which a matting agent is previously dispersed into a coating composition and is then coated, and prior to the completion of drying, a matting agent is sprayed. When plural matting agents are added, both methods may be employed in combination.
Sensitizing dyes are applicable to the light-sensitive layer of photothermographic materials used in this invention, including those which are described in JP-A 63-159841, 60-140335, 63-231437, 63-259651, 63-304242, 63-15245; U.S. Pat. Nos. 4,639,414, 4,740,455, 4,741,966, 4,751,175 and 4,835,096. Further, sensitizing dyes usable in this invention are described in Research Disclosure item 17643, IV-A, page 23 (December, 1978) and references cited therein. Sensitizing dyes exhibiting spectral sensitivity specifically suitable for spectral characteristics of various scanner light sources can be advantageously selected. There can be selected, for example, simple merocyanines described in JP-A No. 60-162247 and 2-48635, U.S. Pat. No. 2,161,331, German Patent No. 936,071, and Japanese Patent Application No. 3-189532, which are suitable for an argon ion laser light source; three-nuclei cyanine dyes described in JP-A No. 50-62425, 54-18726, 59-102229 and merocyanine dyes described in Japanese Patent Application No. 6-103272, which are suitable for a helium-neon laser light source; thiacarbocyanine dyes described in JP-B No. 48-42172, 51-9609, 55-39818 (hereinafter, the term, JP-B refers to published Japanese Patent), JP-A No. 62-284343 and 2-105135, which are suitable for LED light source and infrared semiconductor laser light source; tricarbocyanine dyes described in JP-A No. 59-191032 and 60-80841 and4-quinoline nucleus-containing dicarbocyanine dyes described in JP-A 59-192242 and 3-67242 [formulas (IIIa) and (IIIb)], which are suitable for an infrared semiconductor laser light source. Further, sensitizing dyes described in JP-A No. 4-182639, 5-341432, JP-B No. 6-52387, 3-10931, U.S. Pat. No. 5,441,866 and JP-A 7-13295 are also employed to respond to infrared laser light of not less than 750 nm, preferably not less than 800 nm. These sensitizing dyes may be used alone or in combination thereof. The combined use of sensitizing dyes is often employed for the purpose of supersensitization. A super-sensitizing compound, such as a dye which does not exhibit spectral sensitization or substance which does not substantially absorb visible light may be incorporated, in combination with a sensitizing dye, into the emulsion.
Crosslinking agents usable in the invention include various commonly known crosslinking agents used for photographic materials, such as aldehyde type, epoxy type, vinylsulfon type, sulfonester type, acryloyl type, carbodiimide type crosslinking agents, as described in JP-A 50-96216. Specifically preferred are an isocyanate type compound, epoxy compound and acid anhydride, as shown below. One of the preferred crosslinking agents is an isocyanate or thioisocyanate compound represented by the following formula:
Formula
Xxe2x95x90Cxe2x95x90Nxe2x80x94Lxe2x80x94(Nxe2x95x90Cxe2x95x90X)v 
wherein v is 1 or 2; L is a bivalent linkage group of an alkylene, alkenylene, arylene or alkylarylene group; and X is an oxygen atom or a sulfur atom. An arylene ring of the arylene group may be substituted. Preferred substituents include a halogen atom (e.g. bromine atom, chlorine atom), hydroxy, amino, carboxy, alkyl and alkoxyl.
The isocyanate crosslinking agent is an isocyanate compound containing at least two isocyanate group and its adduct. Examples thereof include aliphatic isocyanates, alicyclic isocyanates, benzeneisocyanates, naphthalenediisocyanates, biphenyldiisocyanates, diphenylmethandiisocyanates, triphenylmethanediisocyanates, triisocyanates, tetraisocyanates, their adducts and adducts of these isocyanates and bivalent or trivalent polyhydric alcohols. Exemplary examples are isocyanate compounds described in JP-A 56-5535 at pages 10-12, including: ethanediisocyanate, butanediisocyanate, hexanediisocyanate, 2,2-dimetylpentanediisocyanate, 2,2,4-trimethylpentanediisocyanate, decanediisocyanate, xcfx89,xcfx89xe2x80x2-diisocyanate-1,3-dimethylbenzol, xcfx89,xcfx89xe2x80x2-diisocyanate-1,2-dimethylcyclohexanediisocyanate, xcfx89,xcfx89xe2x80x2-diisocyanate-1,4-diethylbenzol, xcfx89,xcfx89xe2x80x2-diisocyanate-1,5-dimethylnaphthalene, xcfx89,xcfx89xe2x80x2-diisocyanate-n-propypbiphenyl, 1,3-phenylenediisocyanate, 1-methylbenzol-2,4-diisocyanate, 1,3-dimethylbenzol-2,6-diisocyanate, naphthalene-1,4-diisocyanate, 1,1xe2x80x2-naphthyl-2,2xe2x80x2-diisocyanate, biphenyl-2,4xe2x80x2-diisocyanate, 3,3xe2x80x2-dimethylbiphenyl-4,4,-diisocyanate, diphenylmethane-4,4xe2x80x2-diisocyanate, 2,2xe2x80x2-dimethyldiphenylmethane-4,94-d1socyanate, 3313-dimethoxydiphenylmethane-4,4xe2x80x2-diisocyanate, 4,3xe2x80x2-diethoxydiphenylmethane-4,4xe2x80x2-diisocyanate, 1-methylbenzol-2,4,6-triisocyanate, 1,3,5-trimethylbenzene-2,4,6-triisocyanate, diphenylmethane-2,4,4xe2x80x2-triisocyanate, triphenylmethane-4,4xe2x80x2,4xe2x80x2-triisocyanate, tolylenediisocyanate, 1,5-naphthylenediisocyanate; dimmer or trimer adducts of these isocyanate compounds (e.g., adduct of 2-mole hexamethylenediisocyanate, adduct of 3 mole hexamethylenediisicyanate, adduct of 2 mole 2,4-tolylenediisocyanate, adduct of 3 mole 2,4-tolylenediisocyanate); adducts of two different isocyanates selected from these isocyanate compounds described above; and adducts of these isocyanate compounds and bivalent or trivalent polyhydric alcohol (preferably having upto 20 carbon atoms, such as ethylene glycol, propylene glycol, pinacol, and trimethylol propane), such as adduct of tolylenediisocyanate and trimethylolpropane, or adduct of hexamethylenediisocyanate and trimethylolpropane. Of these, adduct of isocyanate and polyhydric alcohol improves adhesion between layers, exhibiting high capability of preventing layer peeling, image slippage or production of bubbles. These polyisocyanate compounds may be incorporated into any portion of the photothermographic material, for example, into the interior of a support (e.g., into size of a paper support) or any layer on the photosensitive layer-side of the support, such as a photosensitive layer, surface protective layer, interlayer, anti-halation layer or sublayer. Thus it may be incorporated into one or plurality of these layers.
The thioisocyanate type crosslinking agent usable in the invention is to be a compound having a thioisocyanate structure, corresponding to the isocyanates described above.
The crosslinking agents described above are used preferably in an amount of 0.001 to 2 mol, and more preferably 0.005 to 0.5 mol per mol of silver.
Next, the layer arrangement of photothermographic materials used in this invention will be described. The photothermographic material comprises at least one light sensitive layer on a support. There is the light sensitive layer alone on the support or there may be further provided at least a light insensitive layer on the light sensitive layer. To control the amount or wavelength distribution of light transmitted to the light sensitive layer, a filter layer may be provided on the light sensitive layer side or on the opposite side, or a dye or pigment may be incorporated in the light sensitive layer. Dyes used therein are preferably compounds described in JP-A 8-201959. The light sensitive layer may be comprised of plural layers, or the combination of high-speed and low-speed light sensitive layers may be provided. Various additives may be incorporated into the light sensitive layer, light insensitive layer or other component layer(s). Examples thereof include a surfactant, antioxidant, stabilizer, plasticizer, UV absorbent and coating aid.
Next, coating methods relating to the photothermographic material will be described. Coating solutions used for the photothermographic material are preferably filtered prior to their coating. In the filtration, it is preferred to cause the coating solution to pass through a filter material having a absolute or semi-absolute filtering precision of 5 to 50 xcexcm, once or more.
In coating photothermographic materials used in this invention employed are successive coating methods in which coating and drying of each layer are successively repeated, including, for example, a roll coating system such as reverse roll coating and gravure roll coating, blade coating, wire-bar coating, and die coating. A simultaneous multi-layer coating is also employed, in which before a coated layer is dried, the next layer is coated using plural coaters and the thus coated plural layers are simultaneously dried, or plural coating solutions are simultaneously layered and coated using slide coating, curtain coating or an extrusion type die coater having plural slits, in which the latter coating is preferred in terms of prevention of occurrence of coating troubles caused by impurities incorporated from the outside. In the simultaneous multi-layer coating, to prevent cross-layer contamination, the viscosity of the uppermost layer coating solution is preferably not less than 0.1 Paxc2x7s and that of other layer coating solution is preferably not less than 0.03 Paxc2x7s. When coating solutions of two or more layers are layered, a solid content dissolved in one layer which is insoluble in a solvent used in the adjacent layer tends to cause turbulence or turbidity at the interface. It is therefore preferable that major solvents contained in respective layer coating solutions are identical (or the content of a solvent commonly contained in coating solutions is more than other solvents).
After completion of multiplayer coating, it is preferred to dry as promptly as possible and it is more preferred to complete drying within 10 sec. to avoid cross-layer mixing caused by flow, diffusion or density difference. A hot air drying system, an infrared ray drying system and the like are generally employed and the hot air drying system is preferred, in which the drying temperature is preferably 30 to 100xc2x0 C.
The thus prepared photothermographic material may be cut to an intended size and packed immediately after completion of drying, alternatively, the photothermographic material may be wound up on the roll and temporarily stocked prior to cutting and packaging. A wind-up system is not specifically limited but a tension control system is generally employed.
Exposure of the photothermographic material is conducted preferably employing argon laser (488 nm), he-ne-laser (633 nm), red semiconductor laser (670 nm), infrared semiconductor laser (780 nm, 820 nm). Of these, infrared semiconductor laser is preferred in terms of being high power and transparent to the photothermographic material.
In the invention, exposure is preferably conducted by laser scanning exposure. It is also preferred to use a laser exposure apparatus, in which a scanning laser light is not exposed at an angle substantially vertical to the exposed surface of the photothermographic material. The expression xe2x80x9claser light is not exposed at an angle substantially vertical to the exposed surfacexe2x80x9d means that laser light is exposed preferably at an angle of 55 to 88xc2x0, more preferably 60 to 86xc2x0, still more preferably 65 to 84xc2x0, and optimally 70 to 82xc2x0. When the photothermographic material is scanned with laser light, the beam spot diameter on the surface of the photosensitive material is preferably not more than 200 xcexcm, and more preferably not more than 100 xcexcm. Thus, a smaller spot diameter preferably reduces the angle displacing from verticality of the laser incident angle. The lower limit of the beam spot diameter is 10 xcexcm. The thus laser scanning exposure can reduce deterioration in image quality due to reflected light, resulting in occurrence such as interference fringe-like unevenness.
Exposure applicable in the invention is conducted preferably using a laser scanning exposure apparatus producing longitudinally multiple scanning laser beams, whereby deterioration in image quality such as occurrence of interference fringe-like unevenness is reduced, as compared to a scanning laser beam of the longitudinally single mode. Longitudinal multiplication can be achieved by a technique of employing backing light with composing waves or a technique of high frequency overlapping. The expression xe2x80x9clongitudinally multiplexe2x80x9d means that the exposure wavelength is not a single wavelength. The exposure wavelength distribution is usually not less than 5 nm and not more than 10 nm. The upper limit of the exposure wavelength distribution is not specifically limited but is usually about 60 nm.
Photothermographic materials used in this invention are stable at ordinary temperature and are developed upon being heated at a high temperature after exposure. The heating temperature is preferably 80 to 200xc2x0 C., and more preferably 100 to 150xc2x0 C. Heating at a temperature lower than 80xc2x0 C. results in images with insufficient densities and at the heating temperature higher than 200xc2x0 C., the binder melts, adversely affecting not only images but also transportability and a thermal processor. On heating, oxidation-reduction reaction between an organic silver salt (acting as an oxidant)and a reducing agent is caused to form silver images. This reaction process proceeds without supply of water from the outside.